One major problem with known trawl net opening devices is the fact that substantial power is expended in using same. For example, with commonly known trawl-doors which are operated at an angle to the forward motion of the trawl boat, it has been reported by T. Kowalski and J. Giannoti of the University of Rhode Island, Marine Technical Report No. 16, that approximately 44% of the total drag is used by a fishing trawl boat in overcoming the resistance of the trawl doors in operation.
According to the Food & Agriculture Organization of the United Nations, 70% of the commercial fishing of the world employs such well known and conventional trawl-doors in bottom and midwater otter trawl type fishing nets. Other common problems of known type trawl net opening devices is their cumbersome operation, as well as the great number of elements involved which, of course, require constant maintenance and repair and such devices are also relatively expensive and costly.
Another common problem with known type of trawl net opening devices is that because of their cumbersome operation, considerable skill is required in their use and operation.
The following four patents may be pertinent to this invention and are identified as follows:
______________________________________ Y. Matsumura 1,305,483 June 3, 1919 F. J. Luketa 3,281,980 Nov. 1, 1966 Fuhrboter et al 4,052,800 Oct. 11, 1977 Bourret 4,224,755 Sept. 30, 1980 ______________________________________
My invention is based upon the principles of PASCAL and of ARCHIMEDES. Blase Pascal (1623-1662) promulgated the law "Pressure applied to an enclosed fluid is transmitted undiminshed to every portion of the fluid and the walls of the containing vessel." (This is a necessary consequence of the laws of fluid mechanics, rather than an independent principle.)
In a fluid, such as water which is incompressible, a change in pressure of one portion of the fluid is transmitted instantenously to all other parts. Also, changes in temperature accompany changes in pressure in a compressible fluid.
As in an automotive hydraulic jack, since the walls of the hydraulic jack are confining and do not expand, when pressure is introduced to the fluid, the working surface of the jack must lift and raise-up the load or car. Equally in a flexible hose, when pressure of a fluid is introduced within the strength limits of the hose, the hose must tend to become straight and rigid.
ARCHIMEDES principle is also a necessary consequence of the laws of fluid statics. When a body is wholly or partly immersed in a fluid, such as sea-water at rest, the fluid exerts pressure on every part of the body's surface in contact with the fluid. The pressure is greater on the parts immersed more deeply. The resultant of all the forces is an upward buoyancy force of the immersed body.
ARCHIMEDES principle, namely, "that a body wholly or partly immersed in a fluid is buoyed up with a force equal to the force equal to the weight of the fluid displaced by the body". This force acts vertically up through the center of gravity of the fluid before its displacement. The corresponding point in the immersed body is called its center of buoyancy.
In the case of my improved trawl net, normally used floats, rollers, wheels and chains are used as required. Also, a pressure compensating release can be incorporated on the fill/release valve to aid in depth compensation. When trawling depths are known, pressure can be adjusted in the hose ahead of time, thus saving considerable time over adjustments needed when trawling with conventional trawl doors.